New or used tea leaves are good for growing roses. Tea leaves can also be used to help lower the soil's pH. Soil high in pH can become great breeding grounds for rust fungus species that can ruin rose bushes.
Tea leaves contain tannic acid, which is the ingredient rose bushes need to help fight rust fungus as well as for growth. Master gardener and author Jerry Baker also claims that tea can help rose bushes regrow after pruning.
Black tea or green tea can be used since both contain tannic acid or tannins. Ordinary black tea, called orange pekoe, is recommended by "A Garden for Life: A Natural Approach to Designing, Planting and Maintaining a North Temperate Garden."
Tea leaves, in bags or loose, can be placed on the soil after pruning. They can also be placed in the early spring before the roses begin growing.